1. Field of the Invention
The present invention relates to an initial firing method and a phase change memory device, and more particularly, to an initial firing method and a phase change memory device capable of effectively performing an initial firing operation in order to perform a stable read-out operation.
2. Description of the Related Art
An “initial firing” operation is an operation for initially applying a high current to a phase change memory device having phase change materials after its production. The initial firing generates sufficient heat at a contact interface between the phase change materials, so that the phase change materials have a uniform resistance distribution.
FIG. 1 is a view illustrating a set resistance distribution of a phase change material before it is subjected to the initial firing operation
Referring to FIG. 1, in the range (i), the set resistance values are widely distributed and the average set resistance value is high. Therefore, at the time of the read-out operation, defects may occur, and thus, the yield may be reduced.
FIG. 2 is a view illustrating the set resistance distribution of a phase change material after it is subjected to the initial firing operation.
Referring to FIG. 2, in the range (ii), the set resistance values are narrowly and uniformly distributed and the average set resistance value is lower than that of the phase change material before it is subjected to the initial firing operation.
The initial firing operation is needed in order to perform the stable read-out operation of the phase change memory device. The initial firing operation is a mandatory test operation that is performed on a wafer only once.
Conventionally, the initial firing operation is performed on each phase change memory cell individually. Therefore, there is a problem that, as the number of phase change memory cells on the wafer increases, testing becomes more time-consuming.